The LCD (Liquid Crystal Display) possesses many advantages of being ultra thin, power saved and radiation free. It has been widely utilized in, such as LCD TVs, mobile phones, Personal Digital Assistant (PDA), digital cameras, laptop screens or notebook screens, and dominates the flat panel display field.
Most of the liquid crystal displays on the present market are backlight type liquid crystal displays, which comprise a liquid crystal display panel and a backlight module. The working principle of the liquid crystal display panel is that the Liquid Crystal is injected between the Thin Film Transistor Array Substrate (TFT array substrate) and the Color Filter (CF). The light of backlight module is refracted to generate images by applying driving voltages to the two substrates for controlling the rotations of the liquid crystal molecules.
The liquid crystal display panel comprises a plurality of pixels arranged in array. Each pixel is electrically coupled to one thin film transistor (TFT), and a gate (Gate) of the TFT is coupled to a horizontal scan line, and a drain is coupled to a vertical data line, and a source is coupled to a pixel electrode. The enough voltage is applied to the level scan line, and all the TFTs electrically coupled to the scan line are activated. Thus, the signal voltage on the data line can be written into the pixel to control the transmittances of liquid crystals to achieve the display effect.
The liquid crystal molecules have a certain property, which is that the liquid crystal molecules will be polarized if the voltage of the same direction is applied to the liquid crystal molecules with a long period of time. Even the voltage disappears, the property of the liquid crystal molecules will be destroyed and can no longer be rotated due to the variation of the electrical field. Therefore, the liquid crystal display panel must be driven alternately. As showing images, the liquid crystal molecules are rotated with a certain frequency to prevent that the liquid crystal molecules fixedly lean to the same direction and lose the activity. At present, the liquid crystal display panel supports the multiple inversion modes, such as dot inversion mode, row inversion mode, column inversion mode, and etc. The way of achieving the inversion is mainly to constantly alter the positive, negative polarities of the source voltage of the TFT (i.e. the positive, negative polarities of the signal voltage), or constantly alter the positive, negative polarities of the common electrode to realize the objective of the alternate drive. When the liquid crystal display panel normally functions, the voltage difference between the positive, negative source voltages of the TFT (i.e. the signal voltage) and the gate voltage are different, and thus, in the same period of time, the charge effects of the TFT sources to the pixels shows to be different. Accordingly, the brightnesses of respective pixels in the display image differ. Ultimately, the image display effect is nonuniform.
FIG. 1 is a circuit diagram of a liquid crystal display panel of column inversion driving mode according to prior art, and FIG. 2 is a sequence diagram of the circuit shown in FIG. 1. Please refer to FIG. 1. The liquid crystal display panel of column inversion driving mode according to prior art comprises a plurality of data lines, which are mutually parallel, sequentially aligned and vertical, a plurality of scan lines, which are mutually parallel, sequentially aligned and horizontal and a plurality of pixels arranged in array, and each pixel comprises a pixel driving circuit inside; all the plurality of pixel driving circuits in the pixels of the same row are electrically coupled to the scan line corresponding to the pixel of the row; all the plurality of pixel driving circuits in the pixels of the same column are electrically coupled to the data line corresponding to the pixel of the column. The pixel driving circuit comprises: a driving thin film transistor T1, and a gate of the driving thin film transistor T1 is electrically coupled to the scan line corresponding the row where the pixel is, and a source is electrically coupled to the data line corresponding the column where the pixel is, and a drain is electrically coupled to one end of a storage capacitor CST1 and one end of a liquid crystal capacitor CLC1; the storage capacitor CST1, the other end of the storage capacitor CST1 is electrically coupled to a common electrode VCOM; the liquid crystal capacitor CLC1, and the other end of the liquid crystal capacitor CLC1 is electrically coupled to the common electrode VCOM. Because the liquid crystal display panel shown in FIG. 1 utilizes column inversion driving mode, referring to FIG. 3, FIG. 4, the polarities of source voltages of the driving thin film transistors T1 in the pixels of every two adjacent columns are opposite, and the polarities of source voltages of the driving thin film transistors T1 in the same pixel for every two adjacent frames are opposite. Specifically, with combination of FIG, FIG. 2, the driving procedure of the liquid crystal display panel of column inversion driving mode according to prior art showing a frame: the plurality of scan lines sequentially scan row by row, and N, M are set to be positive integers. As scan is performed to the Nth scan line, the Nth scan line provides a scan signal GATE(N) to the gates of the driving thin film transistors T1 of the pixels of Nth row, and all the driving thin film transistor T1 of the pixels of Nth row are activated. For the pixels of adjacent Mth column and M+1th column, the Mth data line S(M) writes positive voltage into the source of the driving thin film transistor T1 of Nth row, Mth column, and the length of the writing period is t; the M+1th data line adjacent to the Mth data line S(M) writes negative voltage into the source of the driving thin film transistor T1 of Nth row, M+1 th column, and the length of the writing period is also t; because the polarity of the source voltage of the driving thin film transistor T1 of Nth row, Mth column is positive, and the polarity of the source voltage of the driving thin film transistor T1 of Nth row, M+1th column is negative, and the gate voltages of the driving thin film transistors T1 of Nth row, Mth column and the Nth row, M+1th column are the same, the voltage difference formed by the source voltages of the driving thin film transistors of the pixels of Mth column, M+1th column and the gate voltage are different. Under the circumstance that the pixel charge periods of the pixels of Mth column, M+1th column are the same (both are t1), the charge effects of the pixels of the two columns are different. The display brightnesses of the pixels of Mth column and M+1th column differ. Ultimately, the image display effect is nonuniform.